On page 123, FIG. 60, in the book Herstellung der Wicklungen elektrischer Maschinen by H. Sequenz (Springer-Verlag/Wien 1973), there is shown an undivided stator coil which is arranged in two radially inwardly-facing slots provided in an annular stator core intended for a rotating AC machine, which stator coil differs from the coil type mentioned in the introduction by the fact that the two coil halves constitute integral parts of a unitarily manufactured coil and are thus not connected together with the aid of a special connection piece.
In conventional coils formed from two interconnected coil halves, for example the coil shown in U.S. Pat. No. 3,344,297 and the coil shown in German Pat. No. 932.972, the two coil halves are made with substantially the same shape as the coil halves of the above-mentioned coil shown in the book, whereas the outermost part of the coil end is replaced by the above-mentioned special connection piece. Each of the two series-connected coil end halves--which together constitute a coil end--is constructed in such a way that the radial distance to the air gap has its smallest value near the winding slot and then increases with increasing axial distance from the end surface of the annular stator core, whereby the maximum increase of the radial distance is greater with the bottom coil end half than with the top coil end half. The radially outwardly-directed surfaces of all the top coil end halves and the radially inwardly-directed surfaces of the bottom coil end halves are then positioned in a radially inner and a radially outer imaginary, conical surface, respectively. In the same manner as with corresponding stator windings comprising unitarily manufactured coils only, these surfaces are formed with a space between them in order to achieve sufficient ventilation and sufficient safety against flash-over.
When unitarily manufactured coils are used, the top coil end halves--which constitute integral parts of the coils--are formed in such a way that they are lying in an conical surface which is tapering in a direction towards the stator core, which is advantageous since a tapering of this kind often reduces the risk of damaging the stator winding during the insertion of a rotor into the stator.
Also the machines disclosed in the patent specifications mentioned above are made with their top coil end halves lying in a conical surface which is tapering towards the stator core.